The narrative ignites with the brutal, soul-crushing betrayal of Issei Hyoudou by Rias Gremory and his entire peerage, who cast him aside for new lovers, deeming him a "lazy pervert" despite his silent sacrifices and fervent desire to propose. This emotional devastation, coupled with the corruption of his devil pieces, pushes him to the brink of death, activating a hidden power within. Ddraig, his loyal dragon partner, guides him through a harrowing process of forcefully removing the evil pieces, a feat deemed impossible and suicidal. Against all odds, Issei endures an agonizing transformation, shedding his human and devil forms to emerge as a nascent True Dragon of Domination, his body honed, his senses heightened, and his appearance strikingly handsome, now possessing a unique "Aura" of dominance. Transported inadvertently to Lady Death's domain, he confronts the ultimate arbiter of life and death, an entity scarred by her own past betrayals. Their initial clash of wills, sparked by her possessive advances and his defiant refusal to be claimed, quickly morphs into a profound connection as they recognize shared pain. Lady Death, now renamed Semiramis by Issei, sees in him a pure soul capable of true love, offering her mentorship and the promise of Ddraig's physical resurrection, a development that will forever alter the balance of power in his original world and beyond.

Following his rebirth and initial training with Semiramis and Scathach, Issei is unexpectedly thrust into the chaotic world of Konosuba, a realm far removed from his previous life's struggles. Here, he inadvertently assembles a party of eccentric adventurers, starting with the shy but powerful Arch Wizard Yunyun, whom he treats with genuine kindness, earning her unwavering loyalty and affection. His overwhelming strength, initially masked by a hood to avoid unwanted attention, quickly becomes apparent as he effortlessly dispatches high-level monsters and earns the moniker "Tyrant Overlord." He expands his unconventional harem, drawing in the undead Lich Wiz with his compassion and understanding, offering her solace from her existential loneliness. The addition of the dysfunctional trio of Kazuma, Aqua, and Megumin, along with the masochistic Crusader Darkness, creates a whirlwind of comedic chaos, yet Issei's quiet strength and unwavering moral compass guide them through their misadventures. Despite their constant debt and bizarre antics, Issei's presence elevates them, subtly reshaping their destinies while he hones his rapidly evolving powers, including advanced elemental magic and unique aura-infused skills, all while remaining oblivious to the full extent of his charm.

Issei's journey continues into the realm of Evenicle, a world governed by Mother Eve's strict commandments, where he meets the twin Dragonkin Kyou and Kinou. Having lost his memories after a brutal encounter with Nyarlathotep, he is nursed back to health by the twins, who, recognizing his dragon nature and pure heart, mark him as their mate. His memories return through an encounter with QD, the Queen Dragon, revealing his past and the cosmic scale of his previous battles. To marry Kyou and Kinou, Issei must become a Knight, a privileged class allowed multiple spouses. He quickly ascends the ranks, demonstrating unparalleled strength and earning the respect of figures like Acheval and Barro. Along this path, he encounters and marries Ramius, a dedicated but insecure Knight, and Riche, a spirited princess fighting the shadowy Snake Crest organization. Issei's unwavering kindness, formidable power, and commitment to justice draw these women into his orbit, forming a loyal and powerful family dedicated to him, even as he confronts political intrigue, monstrous threats, and the lingering influence of his past enemies.

A pivotal moment of profound challenge and self-discovery unfolds when Issei, experimenting with his evolving spatial magic, inadvertently creates a rift black hole and is pulled into the dimensional void. There, he confronts Nyarlathotep, the Outer God of Chaos, a being of incomprehensible power that he barely survived in a previous, unremembered encounter. Despite his immense growth, Issei is outmatched, pushed to his absolute limits in a desperate battle. Forced to unleash a dangerous, unmastered skill that transforms him into a humanoid dragon, he manages to wound the primordial entity before succumbing to unconsciousness. Nyarlathotep, intrigued by Issei's raw potential and the rare ability to injure it, marks him with its "Chaos" element and returns him to the Evenicle world, where he is found by Kyou and Kinou, his memory erased as a consequence of the battle. This memory loss, though temporary, highlights the cosmic dangers he faces. His subsequent regaining of memories in Camelot, triggered by the mention of Semiramis, fully reconnects him to his shattered past, allowing him to integrate his DxD origins with his new life and accelerating his mastery of the Chaos element, preparing him for future confrontations and cementing his destiny as a true Dragon King.